Nobody is saying "StackOverflow gives you a one-click tool to create their competitor sites!" They're just saying that 1) SO has made it impossible for themselves to set up a paywall around the content and 2) if they go evil, it's POSSIBLE to take your data and leave. The fact that they have open sourced some of their tools and that competing frameworks already exist make this easier, but no, still not easy.

But is that SO's fault? What more could SO do to earn your trust? And what alternative to SO do you propose?